During resection of tissue, particularly of tumor tissue in the gastrointestinal tract, that is restricted to the mucosa, excision should be carried out, where possible, in one session and as fully as possible. Conventionally, for this purpose, the snare technique or the cap technique are used, wherein, depending on the snare diameter or the cap diameter, circular excisions of varying size are produced.
In order to be able to excise large-area tumours with a diameter of more than eight centimeters in one session and as completely as possible, it is proposed, for example, in WO 2006/108480 A1 that, during endoscopic mucosa resection, fluid is first injected under the mucosa through a flexible needle before the resection. For this, the needle is inserted into the submucosa. Due to the penetration of the fluid into the mucosa, it becomes separated from the muscularis propria, so that a fluid cushion is produced under the mucosa. This creates a safe separation from the muscularis propria as well as provides thermal protection. The mucosa resection is then performed using, for example, a flexible discission needle, and particularly a high-frequency surgical instrument. Alternatively, the prior art also discloses resection by means of argon plasma coagulation.
With the water jet surgical instrument of the prior art, a concentrated water jet emerges at the distal end of the instrument under high pressure and penetrates the soft mucosa. In the submucosa (in the elastic fibrous displaceable layer) the penetrating fluid collects so that a fluid cushion is produced. For this type of selective tissue separation according to the prior art, a fluid jet with a high water flow rate and a high speed is used. Due to the geometry, a laminar water jet having the diameter of the nozzle is produced at the nozzle outlet.
It is considered problematic that during endoscopic submucosal dissection of this type, a perforation of the muscularis propria (referred to simply as ‘muscularis’ below) by the water jet can occur. This, in turn, can lead to dangerous internal bleeding which also hinders the view of the surgeon, so that rinsing of the operation site has to be carried out. This requires removal of the instrument from the operating channel, which involves further delay and further risk to the patient.